The present invention relates to a fluoroelastomer, a process for producing the fluoroelastomer, a crosslinkable composition containing the fluoroelastomer and a curing product from the crosslinkable composition.
Properties such as resistances to heat, cold and solvents (including fuel oil and other oils) are required for molded items such as oil seals and fuel hoses for automobiles, aircrafts, etc. Thus, there is a demand for the development of resin materials which possess these properties in desirable balance.
For example, Japanese Patent Publication No. 54(1979)-1585 describes a fluorinated polymer composition comprising an organic peroxide and a fluorinated polymer obtained by copolymerization with an olefin containing 3 mol % or less of bromine. However, the product of peroxide crosslinking obtained from this composition, although exhibiting cold resistance to a certain extent, has a drawback in that the solvent resistance is poor.
On the other hand, Japanese Patent Publication No. 58(1983)-4728 describes a fluorinated multisegmented polymer obtained by copolymerization with the use of an iodated compound as a chain transfer agent. However, because the iodated compound used as a chain transfer agent has a small molecular weight, there is a problem that an improvement of cold resistance cannot be expected at all.
The inventors have made extensive and intensive studies with a view to solve the above problems of the prior art. As a result, it has been found that, when use is made of a crosslinkable composition containing a specified fluoroelastomer, there can be obtained a curing product which is excellent in resistances to heat, cold and solvents. The present invention has been accomplished on the basis of this finding.
An object of the present invention is to solve the above problems of the prior art. Specifically, objects of the present invention are to provide a fluoroelastomer from which a curing product excellent in resistances to heat, cold and solvents, can be obtained and to provide a crosslinkable composition containing the same and a curing product therefrom.
The fluoroelastomer of the present invention comprises:
constituent units derived from vinylidene fluoride (a), and
constituent units derived from perfluoro(methoxypropyl vinyl ether) (b),
optionally together with constituent units derived from tetrafluoroethylene (c) and/or constituent units derived from a perfluoroalkyl vinyl ether (d),
wherein:
the constituent units (a) are contained in an amount of 65 to 85 mol %,
the constituent units (b) are contained in an amount of 0.5 to 30 mol %,
the constituent units (c) are contained in an amount of 0 to 10 mol %, and
the constituent units (d) are contained in an amount of 0 to 25 mol %.
It is preferred that the constituent units (b) be contained in an amount of 6 to 25 mol %.
The fluoroelastomer of the present invention may further comprise constituent units (e) derived from a brominated compound, iodated compound or iodated brominated compound represented by the general formula:
RBrnIm xe2x80x83xe2x80x83[I]
wherein R represents any of a fluorohydrocarbon group, a chlorofluorohydrocarbon group, a chlorohydrocarbon group and a hydrocarbon group, these groups optionally having a functional group X, X representing xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x95x90NR, xe2x80x94COOH, xe2x80x94SO2, xe2x80x94SO3H or xe2x80x94PO3H; and each of n and m is 0, 1 or 2.
The above constituent units (e) are preferably contained in an amount of 0.001 to 5 parts by weight per 100 parts by weight of the sum of the constituent units (a), (b), (c) and (d).
The process for producing a fluoroelastomer according to the present invention comprises copolymerizing vinylidene fluoride and perfluoro(methoxypropyl vinyl ether), optionally together with tetrafluoroethylene and/or a perfluoroalkyl vinyl ether, in the presence of a compound represented by the general formula:
RBrnIm xe2x80x83xe2x80x83[I]
wherein R represents any of a fluorohydrocarbon group, a chlorofluorohydrocarbon group, a chlorohydrocarbon group and a hydrocarbon group, these groups optionally having a functional group X, X representing xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x95x90NR, xe2x80x94COOH, xe2x80x94SO2, xe2x80x94SO3H or xe2x80x94PO3H; and each of n and m is 0, 1 or 2.
The crosslinkable composition of the present invention comprises the above fluoroelastomer and a peroxide crosslinking agent. The curing product of the present invention is produced by curing this crosslinkable composition.